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Biamping Cambridge Audio

Discussion in 'Audio Processors & Power Amps' started by IvanFraser, Oct 28, 2011.

  1. IvanFraser

    IvanFraser Member

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    This one's for Arfur, if you're reading this, or anyone else who has the CA p500 power amps.

    The manual shows when biamping to wire the HF amp AND the LF amp on the lower (LF) speaker terminals. Whereas when bi-wiring it says to use the lower set of posts for LF and the higher posts for HF.

    Manual is localted here: http://www.cambridgeaudio.com/assets/documents/AP105134CAAmplifiersUsersManual.pdf

    When single amp was used and biwired, it was smooth and great sounding - well-balanced.

    My biamped kit however sounds like it's top end-heavy when wired this way, like there's disproportionately more HF than bass/mid, and the mid can sound harsh on some music, as well as speech. I've lived with it for a couple of weeks - hoping it'll settle in, but I doubt that a louder HF amp would suddenly get significantly quieter, even if the bass amp warms up (would it get louder? to match? - is there a weird gain discrepancy between these 2 supposedly identical amps? I have no idea)

    Could it be the manual is wrong?

    Should the HF amp be using the HF speaker terminals?

    I don't want to rewire the HF terminals on the speakers to the HF terminals on the amp, just in case it may cause damage if I'm wrong.

    Does anyone know for sure that the manual is correct? I've known them be wrong before.

    Also the manual shows 2 pre-outs for the preamp, and specifically shows the HF outputs from one set and LF from the other, but does not explain if this is a necessity. If both pre outs carried identical signals, it wouldn't matter which you used for which amp. And I've found that wiring them in the other way sounds better. Again, is this correct, or can I cause damage if I wire it up that way? (are pre outs for biamping designed to take LF and HF seperately, or do they just output both equally in these older amps?)

    Arfur, how do you wire your P500 with the A500 - are you using the HF posts from the A500 with the LFs from the P500, or are both wired to the lower posts? Would greatly appreciate the benefit of your experience if you would be so kind.

    All the best

    Ivan
  2. IvanFraser

    IvanFraser Member

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    Oh what a difference a day makes!

    Suddenly, in the middle of a heavy percussive track - Dream Theater - the cymbals, hi hat and harsh sibilant vocals changed from 'in your face' to right back into the mix.

    Most impressive example of amp 'burn-in' I have witnessed.

    2 weeks it's taken. I didn't think it would happen considering I'm now using 2 power amps, and one seemed twice as loud as the other. Of course, another set of interconnects has to be taken into account, as well as using a pre-out that hadn't been used before on a 7 year-old amp.

    For those who believe burn-in is a myth, or psychosomatic, I couldn't disagree more. Nor the idea that biamping makes no difference. In the case of the kit I have, everything has improved - for now, at least :0)

    And re the above question about which terminals to use: a fair bit of Googling gave me the answer that yes, in biamping, the amps are connected in parallel with the full-range signal coming from both outs at the pre-amp to both powers and out of the main posts into the speakers. It's at the speaker end that HF and LF is decided. So it doesn't matter which set of pre-outs I use - which way round they are connected, as both outputs are equal. Only in biwiring a single power amp do we use the LF posts and the HF ones.

    Cheers
    Ivan
  3. formbypc

    formbypc Member

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    There's multiple variations in the manual - which are you following?
  4. IvanFraser

    IvanFraser Member

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    Hi

    I tried the series setup - c to p then to the other p - and it exaggerated the issue, so used the parallel setup, both preouts of the c500 to a p500 each. but basically i've used all possible variations on that theme, different cables etc.

    Seems to be settling down now though.

    Cheers
    Ivan
  5. formbypc

    formbypc Member

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    ...and which Dream Theater track was it?
  6. IvanFraser

    IvanFraser Member

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    I think it was The Answer from Octivarium

    Listening last night I noticed that whilst the harsh lower end of the HF has receded, there's still an excess of high end HF, which is only noticeable occasionally if the source has that part of the spectrum in the mix.

    Not nearly as annoying now though :)
  7. IvanFraser

    IvanFraser Member

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    Nope, it's This Dying Soul, from Train of Thought.

    Sounds much better this morning - much 'balls and chunk'. Cymbals and hi hat back where they should be :)
    Last edited: Oct 30, 2011
  8. Arfa

    Arfa Member

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    Sorry, Ivan, only just found your post!

    I had the A4 and a P500. It was a few years back now. I just took the A4's pre-out to an input on the P500. Canna remember which speaker terminals I used. Shouldn't make any difference mind. The A500, is what I have now in the conservatory, but that's just on its own without P500.

    Are you using same speaker cables for HF and LF? Same interconnects between the C and the two P's?
    Try giving the terminals a clean with some isopropenyl alcohol - may help, possibly...

    It could be some of the capacitors in the amps had aged, and by heavy usage again they've re-formed themselves. Could have been some crap/oxidisation on the terminals, that prevented decent connection. But swapping **** around you inadvertently disturbed it. Also by heavy usage, the current could have broken down the crap and made a decent connection. Urrmm, I'm clutching at straws here! :)
  9. IvanFraser

    IvanFraser Member

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    Thanks Arfur - what you say makes sense.

    There's only a little distortion in the HF left, so cleaning the terminals might help.

    I am using the same cables for the speakers - Chord Rumour4, which I've had for years, and they're on the old amp for the HF. But a second-hand set of Cambridge Studio Reference interconnects on there too to match the ones I have on the LF. I tried other cables - QED (far too bright) and CA AUD500 (not enough detail, restrained), so sought the Studios.

    This constant pulling out of the kit, and rearranging interconnects and cables etc. was driving me (and the missus nuts) :( But every combination seems to sound different. If I use, for example, the 2nd inputs on the power amp the HF separates and exaggerates very noticeably. If I swap the interconnects between the pre-outs it changes again.

    So your thoughts re crap on the terminals makes a lot of sense. They've been sitting there unused for 8 years, some of them. And who knows when or how the other amp and cables were used (especially as the amp comes from a chap who died). The fact that the same input I always used on the original p amp sounds best, and the pre-out 1 too, supports this.

    Thanks for that. :thumbsup:

    Ivan
  10. IvanFraser

    IvanFraser Member

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    Arfur you are indeed 'wise in the ways of science'! :D

    Cleaning all terminals and leads has made a clear difference. I think the harshness has gone - e.g. trumpets on a particularly troublesome track now sound full instead of harsh as though coming from an old tannoy. And vocals aren't as sibillantly harsh - 's's sound like 's's, not whistles, as they were on some female vocals, and speech on tv, hi-hats etc. not too 'topy'.


    Actually, I'm kicking myself that I didn't do this first. :blush:

    Thank you again.

    All the best

    Ivan

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